The present invention relates to a maskless exposure apparatus that does not use a photo-mask to expose a wafer etc., and more particularly to a maskless exposure apparatus that arranges plural fine exposure means.
While the mainstream exposure apparatus projects the entire photo-mask pattern onto the wafer in manufacturing semiconductors, various types of prospective apparatuses have been attempted for a high throughput without the photo-mask. One example is a maskless exposure apparatus that independently controls positions and intensities of plural electron beams using plural electronic optical systems. Another example is a maskless exposure apparatus that arranges fine optical shutters and corresponding fine lenses in an array, opens and closes the shutters while scanning the array, and exposes a desired pattern. Still another example is a maskless exposure apparatus that brings an array of plural fine electrodes into contact with an object to be exposed, or scans the array located above and apart from the object by an extremely small distance, and exposes the object by emitting electrons from fine electrodes.
Commonly to these maskless exposure apparatuses, an exposure unit is formed which arranges plural one-dimensional or two-dimensional exposure means for exposing fine areas, and predetermined exposure areas allocated to these individual fine exposure means. The typical manufacturing process for these maskless exposure apparatuses previously measures an offset of a steady position of each fine exposure means from a reference position.
FIG. 10 is a view showing one illustrative conventional maskless exposure apparatus. FIG. 11 is a top view of a shutter lens array SLA. LS is a light source that generates collimated light. SLA is a shutter lens array that combines shutters and lenses one by one. W is a resist applied wafer. STG is a stage that is mounted with the wafer W and movable in the horizontal and height directions. CTR is a controller that holds pattern information PTN, runs a control program PGM1, and controls opening and closing the shutter and actions of the stage.
B1 is the collimated light generated by the light source LS. S1 is a shutter, which is fixed onto a top plate P1 via a hinge HG1 and opened and closed by a driving mechanism (not shown). A perforation hole H1 extends under the shutter. As the shutter S1 opens, the collimated light B1 reaches the lens L1 and is condensed on the wafer W. The lens L1 is fixed onto a lower plate P2. The shutter lens array SLA is provided with shutters S2 to S9 and lenses L2 to L9 having similar structures, and forms a 3×3 matrix. In FIG. 10, the shutter S3 opens and the condensed beam B2 reaches the wafer W.
A fundamental operation will be described with reference to FIG. 12. SU denotes a unit exposure area on the wafer W, which can be exposed by scanning of the shutter lens array SLA. F1 to F9 are exposure spots of condensed beams available as the shutters S1 to S9 open. SA01 to SA09 are exposure allocated areas corresponding to the shutters S1 to S9, where it is assumed that the exposure spots F1 to F9 have no positional offsets. The exposure allocated area that has no positional offset is referred to as an ideal exposure allocated area. Each of the exposure allocated area SA01 to SA09 is divided into 4×4 pixels, and exposed by arranging the exposure spot of the condensed beam at each pixel position. The exposure allocated area SA01 in FIG. 12 shows this state. For each pixel, a positional offset amount of the exposure spot is measured and the exposure spot is scanned.
In order to arrange the exposure spot of the condensed beam at a desired position, the shutter lens array SLA is moved zigzag along a unit driving curve R. The controller CTR opens and closes the shutters S1 to S9 in accordance with stored exposure pattern information PTN, exposing an arbitrary pattern in the unit exposure area SU. The control program PGM1 obtains data of the unit exposure area SU from the exposure pattern PTN based on the current position on the wafer W, and the data is divided into nine segments corresponding to the exposure allocated areas SA01 to SA09. The control program PGM1 opens and closes the shutters at proper timings based on the divided data while moving the shutter lens array along the unit driving curve R. Since each exposure allocated area is divided into 4×4 pixels, the total number of openings becomes 16. The wafer stage STG is driven along a global driving curve RG whenever the unit exposure area SU is exposed, thereby exposing the entire wafer W. This is the fundamental operation process.
A description will now be given of a positional offset of an exposure spot. A cause of this positional offset includes manufacture (or arrangement) errors of the shutter lens array, such as inclined attachment positions of the lenses L1 to L9. For example, as shown in FIG. 13 where it is assumed that the exposure spots F2 and F5 have positional offsets, the exposure spot F2 shifts by one pixel in the Y direction and the exposure spot F5 shifts one pixel in each of the X and Y directions. Then, the shutter opening/closing control timing as that used for no positional offset exposure results in the defective exposure. For example, the exposure spot F5 shifts from the original position the pattern that is to be exposed on the exposure allocated area SA05 and part of the pattern overlaps the exposure allocated area SA08. Accordingly, when the positional offset of the exposure spot is found beyond the permissible range, the exposure unit is disposed or reassembled to reduce the offset amount and prevent defective exposure.
Prior art includes PCT National Phase Application No. 2003-515255, and U.S. Pat. No. 5,900,637.
As discussed, the conventional maskless exposure apparatus needs a disposal or a reassembly of the entire unit when the exposure means contains a large offset amount, lowering the yield and increasing the cost of the exposure apparatus. When the arrangement of the exposure means offsets due to the time variations, the entire exposure unit is also disposed or reassembled. Therefore, there is a demand for an exposure apparatus that can maintain the highly precise exposure even when each exposure means has a positional offset, and does not require a disposal and reassembly of the exposure unit.